decades for the fbi to locate and arrest the unabomber, ted kaczynski. within the last hour nbc news has confirmed a letter bomb -- not a letter. i should say a letter that tested positive for ricin or some other toxic substance was addressed to senator roger wicker of mississippi. it was intercepted before reaching the senator's office. let's begin this hour with nbc justice correspondent pete williams and former cia counterterrorism director larry johnson. two best guests we could have. pete, let's go back to that picture we just saw from whdh up there, boston affiliate of nbc. what are the experts making of the fact that it was there, that bag, whatever it is sitting there before the explosion and then in this picture taken afterwards you can see the smoke trailing up to the left there diagonally? what does that tell us? >> it tells us it's something they're investigating, chris. they know, they believe very strongly that the bombs were brought to the scene in backpacks. but i think it's fair to say they're looking at whether after they got there, they put them in these shopping bags.